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A silicon micromachining process has been developed to fabricate high-aspect-ratio coplanar waveguide (hicoplanar). A new closed-form analytical transmission line model that is valid for both conventional coplanar waveguide (CPW) and hicoplanar is introduced and compared with simulations and experimental results. The major novelties of the model are that it includes the effect of the conductor height on the output parameters and combines Wheeler's inductance rule and perturbation theory to predict the line resistance. Transmission lines with characteristic impedances of 18-25 Ω have been fabricated on high-resistivity silicon. Attenuation was measured to be 2.4-3.4 dB/cm at 30 GHz before silicon removal and 1.7-2.4 dB/cm at 30 GHz after silicon removal. The analytical model is compared with Ansoft High Frequency Structure Simulator simulations and experimental data and shows excellent agreement.